Alignment film additive, alignment film and liquid crystal display panel

Abstract

The invention relates to an alignment film additive, an alignment film and a liquid crystal display panel, the alignment film additive has a structure as shown in a formula I: # imgabs0 #, A is a liquid crystal-like structure capable of improving the liquid crystal alignment property, G1, G2, G3 and G4 are silyl groups as terminal protecting groups; the alignment film additive provided by the invention can improve the mechanical property of the alignment film, improve the anchoring force of the alignment film to the liquid crystal, and effectively improve the display effect of the liquid crystal display panel.

Description

Technical Field

[0001] The present application relates to the field of displays, and particularly to an alignment film additive, an alignment film, and a liquid crystal display panel. Background Art

[0002] In a liquid crystal display panel (LCD), a liquid crystal alignment film plays a role in aligning liquid crystals in a certain direction. Currently, the commonly used liquid crystal alignment material in the industry is polyimide (PI), and its mainstream alignment method is photo-cleavage and rubbing. In recent years, with the continuous popularization of small movable display terminals such as smart phones, tablets, and notebook computers, the requirement for the high quality of liquid crystal display panels is higher than ever. As a movable display, collisions are inevitably generated during movement. During the collision, the post spacers (PS) in the liquid crystal display panel will move, scratch the PI, and then debris will fall off; in addition, insufficient anchoring force will appear in the scratched area of the PI, and both will cause the generation of bright spots.

[0003] In order to prevent the generation of bright spot defects in the liquid crystal display panel during the collision, the mechanical strength of the liquid crystal alignment film can be improved. As a method for improving the mechanical strength of the liquid crystal alignment film, currently, it is usually to add a crosslinkable additive to the PI to induce crosslinking between molecular chains, thereby improving the mechanical strength of the PI film. However, the currently used crosslinkable additives can improve the strength of the liquid crystal alignment film to a certain extent, but will reduce the alignment property of the liquid crystal. The liquid crystal alignment film with low alignment property will cause afterimages under long-term AC driving of the liquid crystal display panel, reducing the display effect. Summary of the Invention

[0004] The present application provides an alignment film additive, an alignment film, and a liquid crystal display panel. The alignment film additive provided by the present application can improve the mechanical strength of the alignment film while enabling the alignment film to have a high alignment property.

[0005] The present application provides an alignment film additive, and the alignment film additive has a structure shown in Formula I:

[0006]

[0007] Wherein,

[0008] A is selected from the group represented by Formula II,

[0009]

[0010] is selected from a benzene ring, cyclohexane, or cyclohexene, Any H on it is unsubstituted or substituted by F, Cl, Br, -OH, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms;

[0011] Z1, Z2, Z3, Z4, Z5 are selected from a single bond, -O-, -S-, -CO-, -C(O)O-, -OC(O)-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, or an alkylene group having 1 to 10 carbon atoms, or any combination thereof. One or more H atoms in Z1, Z2, Z3, Z4, and Z5 are unsubstituted or substituted by F, Cl, Br, or I;

[0012] n and m are selected from integers from 0 to 10, and n + m ≥ 1;

[0013] B1, B2, B3, B4 are selected from alkylene groups having 1 to 5 carbon atoms;

[0014] G1, G2, G3, G4 include silyl groups.

[0015] In some embodiments, G1, G2, G3, G4 are selected from the groups represented by Formula III,

[0016]

[0017] wherein R1, R2, R3 are selected from alkyl groups having 1 to 10 carbon atoms.

[0018] In some embodiments, R1, R2, R3 are selected from methyl groups.

[0019] In some embodiments, A is selected from the group represented by Formula II-1:

[0020]

[0021] wherein,

[0022] Z1 is selected from a single bond, -O-, -CO-, -C(O)O-, -OC(O)-, -CH2O-, -OCH2-, or an alkylene group having 1 to 5 carbon atoms. One or more H atoms in Z1 are unsubstituted or substituted by F, Cl, Br, or I;

[0023] n and m are selected from 1, 2, or 3;

[0024] p and q are selected from 1, 2, 3, 4, or 5.

[0025] In some embodiments, A contains at least one of phenoxy and biphenyl.

[0026] In some embodiments, in the structure of Formula I, G1-O-B1 and B2-O-G2 are symmetric with respect to A, and G3-O-B3 and B4-O-G4 are symmetric with respect to A.

[0027] In some embodiments, the alignment film additive has the structure shown in Formula I-1:

[0028]

[0029] The present application also provides an alignment film, which is formed from a composition including an acid anhydride, a diamine, and the alignment film additive as described above.

[0030] In some embodiments, the alignment film additive accounts for 0.1 wt% to 10 wt% of the total mass of the acid anhydride and the diamine.

[0031] The present application also provides a liquid crystal display panel, which includes:

[0032] A first substrate;

[0033] A second substrate disposed above the first substrate, and the second substrate is disposed opposite to the first substrate;

[0034] A liquid crystal layer disposed between the first substrate and the second substrate;

[0035] A first alignment film disposed between the first substrate and the liquid crystal layer; and

[0036] A second alignment film disposed between the second substrate and the liquid crystal layer;

[0037] Wherein, the first alignment film and the second alignment film are the alignment films as described above.

[0038] The present application provides an alignment film additive, an alignment film and a liquid crystal display panel. The alignment film additive provided by the present application has a structure shown in Formula I. The structure of Formula I is an amide compound, including an amide group. The amide group can undergo a polymerization reaction with the precursor polyamic acid of polyimide, forming a cross-linked structure between polyamic acid molecules, thereby improving the hardness of the alignment film. A liquid crystal-like structure A is connected between the two amide groups in the structure of Formula I. The liquid crystal-like structure A can improve the liquid crystal anchoring force of the alignment film, thereby improving the liquid crystal alignment performance of the alignment film. The ends of the structure of Formula I are designed with protecting groups G1, G2, G3, and G4. The protecting group includes a silyl group that can be removed under heating conditions. During the heat treatment of the alignment film, the protecting groups at the ends of the alignment film additive desorb and break under high-temperature conditions, exposing the -O- at the ends. The -O- combines with -H to restore the cross-linking effect, and the cross-linking reaction can proceed smoothly. At a relatively low temperature, the protecting groups at the ends of the alignment film additive will not be removed, thereby inhibiting the cross-linking reaction and reducing the formation of unnecessary cross-linked structures, so as to improve the stability and reliability of the alignment film composition. Therefore, the alignment film additive provided by the present application can improve the mechanical strength of the alignment film while making the alignment film have high orientation, and can improve the reliability and stability of the alignment film. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 1H NMR spectrum of an alignment film additive I-1 provided by an embodiment of the present application;

[0040] Figure 2 Chemical structural formula diagram of an alignment film additive I-1 provided by an embodiment of the present application;

[0041] Figure 3 Schematic diagram of the cross-linked structure of an alignment film provided by an embodiment of the present application;

[0042] Figure 4 Schematic diagram of the structure of a liquid crystal display panel provided by an embodiment of the present application;

[0043] Figure 5 Schematic diagram of the pixel electrode and counter electrode film layer of a liquid crystal display panel provided by an embodiment of the present application;

[0044] Figure 6 Partial schematic diagram of the pixel electrode of a liquid crystal display panel provided by an embodiment of the present application.

[0045] Description of the reference numerals:

[0046] 100, Liquid crystal display panel; 101, First substrate; 102, Second substrate; 103, Liquid crystal layer; 104, Alignment film; 1041, First alignment film; 1042, Second alignment film; 105, Pixel electrode; 1051, First pixel; 1052, Second pixel; 1053, First region; 1054, Second region; 106, Counter electrode; 107, Insulating layer; 111, Acid anhydride; 112, Diamine; 120, Alignment film additive. Detailed implementation manners

[0047] It should be understood that the specific implementation manners described herein are only for the purpose of illustration and explanation of this application, and are not used to limit this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative efforts fall within the protection scope of this application.

[0048] This application provides an alignment film additive, and the alignment film additive has a structure shown in Formula I:

[0049]

[0050] Wherein,

[0051] A is selected from the group represented by Formula II,

[0052]

[0053] is selected from benzene ring, cyclohexane or cyclohexene, Any H on is not substituted, or is substituted by F, Cl, Br, -OH, an alkyl group having 1 to 10 carbon atoms, or an alkoxy group having 1 to 10 carbon atoms;

[0054] Z1, Z2, Z3, Z4, Z5 are selected from a single bond, -O-, -S-, -CO-, -C(O)O-, -OC(O)-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, or an alkylene group having 1 to 10 carbon atoms, or any combination thereof. Among them, one or more H in Z1, Z2, Z3, Z4 and Z5 are not substituted, or are substituted by F, Cl, Br or I;

[0055] n and m are selected from integers from 0 to 10, and n + m ≥ 1;

[0056] B1, B2, B3, B4 are selected from alkylene groups having 1 to 5 carbon atoms;

[0057] G1, G2, G3, G4 include silyl groups, and G1, G2, G3, G4 are used as protecting groups and can be removed under heating conditions.

[0058] In the present application, the alignment film additive has the structure shown in Formula I. The structure of Formula I includes an amide group, and the amide group can undergo a polymerization reaction with the polymerizable groups in the polyamic acid, which is a precursor of polyimide, to form a cross-linked structure between polyamic acid molecules, improving characteristics such as the density and film strength of the alignment film. Therefore, the alignment film additive can effectively enhance the hardness of the alignment film. At the same time, a structure A is connected between the two amide groups in the structure of Formula I. Structure A is composed of a cyclic group such as a benzene ring, cyclohexane or cyclohexene and a bridging group located between the cyclic groups, and has a liquid crystal-like structure. The liquid crystal-like structure A has a structure similar to that of liquid crystal molecules and can be anchored to the liquid crystal molecules through intermolecular forces. Therefore, the alignment film additive can effectively enhance the liquid crystal anchoring force of the alignment film, thereby improving the liquid crystal alignment performance of the alignment film. In addition, the ends of the structure of Formula I include protecting groups G1, G2, G3, and G4. These silyl protecting groups can be removed under heating conditions, that is, the chemical bonds between G1 and O, G2 and O, G3 and O, and G4 and O are broken under heating conditions, thereby removing the terminal protecting groups G1, G2, G3, and G4. At this time, the -O- exposed at the end of the structure of Formula I will combine with -H to form -OH, and the -OH at the end of the structure of Formula I can participate in the cross-linking reaction and react with the polymerizable groups in the polyamic acid to form a cross-linked structure; while at a relatively low temperature, the protecting groups at the ends of the alignment film additive will not be removed, and the terminal protecting groups G1, G2, G3, and G4 of the structure of Formula I can play a protective role to inhibit the cross-linking reaction of the terminal groups of the structure of Formula I. Therefore, the formation of unnecessary cross-linked structures can be reduced, and the stability and reliability of the alignment film can be further improved.

[0059] Among them, the above heating conditions can refer to the heat treatment process of the alignment film, such as the pre-curing and post-curing processes of the alignment film. In these processes, heat treatment is required for cross-linking reactions. At this time, the terminal protecting groups of the structure of Formula I are removed, and the cross-linking groups at the ends of the alignment film additive can be restored, enabling it to smoothly carry out cross-linking reactions and enhancing the hardness of the alignment film; the above relatively low temperature can refer to the temperature during the storage of the composition used to form the alignment film. Since the degradation rate of the composition needs to be reduced during storage, unnecessary cross-linking reactions are reduced, and the stability of the composition is ensured. Therefore, under storage conditions, the terminal protecting groups of the structure of Formula I are not removed, playing a role in protecting the terminal groups to improve the stability and reliability of the composition.

[0060] In addition, for the currently used crosslinkable additives, although they can improve the strength of the liquid crystal alignment film to a certain extent, they will reduce the alignment property of the liquid crystal. The reason is that these crosslinkable additives cannot play an alignment role for the liquid crystal. The polyimide molecular chains are connected through the crosslinkable additives, but there is no structure capable of aligning with the liquid crystal in the crosslinking agent region. Then, this crosslinking agent region cannot exert an alignment effect on the liquid crystal, resulting in a decrease in the liquid crystal alignment property of the alignment film. In the alignment film additive of the present application, the liquid crystal-like structure A is located between two amide groups. After the alignment film additive crosslinks with the polyamic acid, since the liquid crystal-like structure A is in the middle position, it is beneficial to enhance the alignment effect of the alignment film additive region between the polyamic acid molecular chains on the liquid crystal, thereby effectively improving the liquid crystal alignment property of the alignment film.

[0061] Therefore, the alignment film additive provided by the present application can improve the mechanical strength of the alignment film while enabling the alignment film to have a high alignment property, and can enhance the reliability and stability of the alignment property.

[0062] In some embodiments, G1, G2, G3, and G4 are selected from the groups represented by Formula III.

[0063]

[0064] Among them, R1, R2, and R3 are selected from alkyl groups having 1 to 10 carbon atoms.

[0065] In the present application, the group represented by Formula III is a Si-containing thermally removable protecting group. Under heating conditions, the Si-O at the end of the structure of Formula I is easily broken, and the process is simple and easy to implement. For example, at a temperature of 150 °C, the Si-O is broken, and the Si-containing protecting group at the end of the structure of Formula I is desorbed and sublimated at high temperature to be removed.

[0066] Furthermore, when R1, R2, and R3 are selected from methyl groups, the group represented by Formula III is -Si(CH3)3. -Si(CH3)3 is a conventional group, which is easy to prepare and is easily removed under heating conditions, capable of simplifying the process.

[0067] In some embodiments, A is selected from the groups represented by Formula II-1:

[0068]

[0069] Among them,

[0070] Z1 is selected from a single bond, -O-, -CO-, -C(O)O-, -OC(O)-, -CH2O-, -OCH2-, an alkylene group having 1-5 carbon atoms, one or more H in Z1 is not substituted, or is substituted by F, Cl, Br, or I;

[0071] n and m are selected from 1, 2 or 3;

[0072] p and q are selected from 1, 2, 3, 4 or 5.

[0073] In this embodiment, A is a liquid crystal-like structure containing groups such as phenyl, -O-, -CH2-, etc., and is a straight-chain structure, that is, a rod-like structure, which is beneficial to improving the liquid crystal orientation of the liquid crystal-like structure A.

[0074] Furthermore, A may contain at least one of phenoxy and biphenyl to improve the liquid crystal orientation of the liquid crystal-like structure A and further improve the liquid crystal orientation of the alignment film.

[0075] Furthermore, A is selected from the group represented by formula II-1-1:

[0076]

[0077] wherein, p and q are selected from 1, 2, 3, 4 or 5.

[0078] In some embodiments, in the structure of formula I, G1-O-B1 and B2-O-G2 are symmetrical about A, and G3-O-B3 and B4-O-G4 are symmetrical about A, that is, the overall structure of formula I is a symmetrical structure about A. The alignment film additive has a symmetrical structure, which can make the arrangement of polyamic acid molecular chains more regular and compact, make the charge distribution more uniform, reduce the molecular polarization phenomenon, reduce the influence on the charge accumulation and charge release rates, and is beneficial to improving the mechanical strength and liquid crystal orientation of the alignment film.

[0079] Furthermore, the structures of B1, B2, B3 and B4 can be the same, and the structures of G1, G2, G3 and G4 can be the same to make the structure of formula I have a symmetrical structure.

[0080] In one embodiment, the alignment film additive has the structure shown in formula I-1:

[0081]

[0082] Formula I-1 is one of the structures of the alignment film additive represented by formula I. The end of the structure of formula I-1 contains a protecting group -Si(CH3)3. The liquid crystal-like structure A of the structure of formula I-1 contains phenoxy and biphenyl, and the structure of formula I-1 is a symmetrical structure. This alignment film additive can effectively improve the mechanical strength and liquid crystal orientation of the alignment film.

[0083] This application also provides a preparation method of the alignment film additive of formula I-1. The preparation process of formula I-1 is as follows:

[0084] S1. Add hydroquinone and ethyl chloroacetate into the solvent N,N-dimethylformamide (DMF), and add potassium carbonate (K2CO3) and potassium iodide (KI), then carry out the reaction to obtain the intermediate compound M1;

[0085]

[0086] S2. Add the intermediate compound M1 obtained in step S1 into the solvent ethanol (C2H5OH), and add potassium hydroxide (KOH), then carry out the reaction to obtain the intermediate product M2;

[0087]

[0088] S3. Add the intermediate compound M2 obtained in step S2 into the solvent toluene, and add oxalyl chloride and N,N-dimethylformamide (DMF), then carry out the reaction to obtain the intermediate product M3;

[0089]

[0090] S4. Add the intermediate compound M3 obtained in step S3 into the solvent dichloromethane (CH2Cl2), and add bis(trimethylsilyl)ethylenediamine and triethylamine (ET3N), then carry out the reaction to obtain the intermediate product M4;

[0091]

[0092] S5. Add the intermediate compound M4 obtained in step S4 and acetic acid (CH3COOH) into the mixed solvent of acetonitrile (CH3CN) and methanol (CH3OH), then carry out the reaction to obtain the intermediate product M5;

[0093]

[0094] S6. Add the intermediate compound M5 obtained in step S5 and trimethylchlorosilane (Cl-Si(CH3)) into the mixed solution of potassium carbonate (K2CO3) and chloroform, then carry out the reaction to obtain the alignment film additive I-1.

[0095]

[0096] Among them, the characterization results of the alignment film additive I-1 are shown in Figure 1 the nuclear magnetic resonance hydrogen spectrum (1H-NMR) diagram shown, Figure 2 the chemical structural formula of I-1 shown and the nuclear magnetic resonance hydrogen spectrum (1H-NMR) data in Table 1.

[0097] Table 1 Nuclear magnetic resonance hydrogen spectrum of I-1 ( 1 1H-NMR) data table

[0098]

[0099]

[0100]

[0101]

[0102] Among them, in Table 1, benzene represents a benzene ring, methylene represents a methylene group, methy represents a methyl group, alpha represents the α-position of an atom or a group, and beta represents the β-position on an atom or a group.

[0103] The present application also provides an alignment film, which is formed by curing a composition. The composition includes an acid anhydride, a diamine, and the alignment film additive as described above.

[0104] Among them, please refer to Figure 3 , during the polymerization process, acid anhydride 111 and diamine 112 first polymerize to form polyamic acid, and then the polyamic acid and the alignment film additive 120 undergo a cross-linking reaction during heating to generate a cross-linked polymer. During the subsequent curing process, the polyamic acid part in the cross-linked polymer will further cyclize to form polyimide, and finally an alignment film 104 with a cross-linked structure is formed. Among them, the amide group in the alignment film additive represented by Formula I can undergo a polymerization reaction with the carboxyl group in the polyamic acid structure, and the hydroxyl group formed after the terminal silyl group of the alignment film additive represented by Formula I is removed can undergo a polymerization reaction with the carboxyl group in the polyamic acid structure, so that the polyamic acid molecules form a cross-linked polymer through the alignment film additive, thereby improving the mechanical hardness of the alignment film.

[0105] Among them, the synthesis method of forming polyamic acid and polyimide by polymerizing acid anhydride monomers and diamine monomers can refer to the prior art, and the present application does not make any restrictions.

[0106] It should be noted that the composition also includes a solvent for the polymerization reaction and other auxiliary additives commonly used in the art. Specifically, it can refer to the synthesis of polyimide alignment films in the prior art, and the present application does not make any restrictions.

[0107] In some embodiments, in the composition of the present application, the alignment film additive accounts for 0.1 wt% to 10 wt% of the total mass of the acid anhydride and the diamine. Further, the alignment film additive accounts for 0.5 wt% to 5 wt% of the total mass of the acid anhydride and the diamine. When the alignment film additive is within the above range, it can improve the cross-linking effect between the alignment film additive and the polyamic acid, while improving the mechanical strength of the alignment film, ensuring that the alignment film has good orientation.

[0108] The present application also provides a liquid crystal display panel 100. Please refer to Figure 4, the liquid crystal display panel 100 includes a first substrate 101, a second substrate 102, a liquid crystal layer 103, a first alignment film 1041, and a second alignment film 1042.

[0109] The first substrate 101 may be an array substrate, including a first substrate, and a thin film transistor layer located on one side of the first substrate close to the liquid crystal layer 103. Among them, the first substrate may be a rigid substrate, such as glass, or the first substrate may also be a flexible substrate, such as polyimide (PI). The structure of the thin film transistor layer may refer to the prior art, and the present application does not make any restrictions.

[0110] Furthermore, on the side of the first substrate 101 close to the liquid crystal layer 103, there are also a counter electrode 106, an insulating layer 107, and a pixel electrode 105 arranged in a stacked manner. The counter electrode 106 is a patterned whole-surface indium tin oxide (ITO) electrode, the pixel electrode 105 is a patterned comb-shaped ITO electrode, and the insulating layer 107 may be a silicon nitride (SiN) film.

[0111] The second substrate 102 may be a color filter substrate, disposed above the first substrate 101 and opposite to the first substrate 101. The second substrate 102 includes a second substrate, and a color filter layer located on one side of the second substrate close to the liquid crystal layer 103. Among them, the second substrate may be a rigid substrate, such as glass, or the second substrate may also be a flexible substrate, such as polyimide (PI).

[0112] The liquid crystal layer 103 is disposed between the first substrate 101 and the second substrate 102, and the liquid crystal layer 103 realizes the display of the picture by the deflection of liquid crystal molecules.

[0113] The first alignment film 1041 is disposed between the first substrate 101 and the liquid crystal layer 103, and the first alignment film 1041 is formed by polymerizing and calcining a composition including an acid anhydride, a diamine, and the alignment film additive as described above.

[0114] The second alignment film 1042 is disposed between the second substrate 102 and the liquid crystal layer 103, and the second alignment film 1042 is formed by polymerizing and calcining a composition including an acid anhydride, a diamine, and the alignment film additive as described above.

[0115] Furthermore, the liquid crystal display panel 100 further includes a first polarizer and a second polarizer. The first polarizer is disposed on the side of the first substrate 101 away from the liquid crystal layer 103, and the second polarizer is disposed on the side of the second substrate 102 away from the liquid crystal layer 103.

[0116] The following further illustrates the alignment film additive and the alignment film of the present application through specific embodiments.

[0117] 1. Preparation of the alignment film

[0118] Alignment film PI-1: Para-phenylenediamine (monomer A) and 1,3-dimethylcyclobutanetetracarboxylic acid (monomer B) are polymerized at a molar ratio of 50:50 to form polyamic acid, obtaining Composition 1. After calcining Composition 1, alignment film PI-1 is formed;

[0119] Alignment film PI-2: Para-phenylenediamine (monomer A) and 1,3-dimethylcyclobutanetetracarboxylic acid (monomer B) are polymerized at a molar ratio of 50:50 to form polyamic acid, and 3 wt% of alignment film additive Add-1 based on the total mass of monomer A and monomer B is added thereto, obtaining Composition 2. After calcining Composition 2, alignment film PI-2 is formed;

[0120] Alignment film PI-3: Para-phenylenediamine (monomer A) and 1,3-dimethylcyclobutanetetracarboxylic acid (monomer B) are polymerized at a molar ratio of 50:50 to obtain polyamic acid, and additive Add-2 at 3 wt% of the total mass of monomer A and monomer B is added thereto, obtaining Composition 3. After calcining Composition 3, alignment film PI-3 is formed.

[0121] Among them, Add-1 is an alignment film additive provided in this application, and Add-2 is a cross-linking additive in the related art. Among them, the structures of monomer A, monomer B, Add-1, and Add-2 are as shown below:

[0122]

[0123]

[0124] 2. Performance testing

[0125] The above-prepared alignment films PI-1, PI-2, and PI-3 are respectively subjected to mechanical hardness testing and testing during long-term storage; and further, a liquid crystal display panel as Figure 4 shown is prepared, and the long-term AC driving-induced image sticking is tested by long-time AC driving.

[0126] 1) Mechanical hardness testing

[0127] Testing method: Place the alignment films prepared above on the support respectively and fix them to make test pieces. Hold a pencil at a 45° angle to the test piece and draw forcefully without breaking the lead core. Draw uniformly forward about 1 cm at a scratching speed of 1 mm / s. After one scratching, re-grind the tip of the lead core and repeat the test 5 times with a pencil of the same hardness mark. Observe the damage condition of the alignment film. When evaluating, if the substrate or the primer coating film is visible in only 2 or fewer tests out of 5 tests, a pencil with a hardness mark one level higher should be used to conduct the same test. When the damage of the alignment film reaches more than 2 times (per 5 tests), the hardness mark of the pencil at this time can be read, and the hardness mark one level lower than this pencil hardness mark should be noted. Refer to the data in Table 2 for the test results.

[0128] 2) Change in the number of particles

[0129] Testing method: Measure the change in the number of particles ΔEA = EA1 - EA0 for the compositions prepared above respectively. When the change in the number of particles is 30 or less, it indicates that it has uniformity during long-term storage; when the change in the number of particles in the composition is outside the above range, it indicates that a cross-linking reaction has occurred between the alignment additive and the polyamic acid during long-term storage, or a large number of particles are formed due to the decrease in the solubility of the alignment additive itself, and the liquid crystal alignment characteristics of the liquid crystal alignment film prepared therefrom deteriorate or it is not suitable for long-term storage.

[0130] Among them, EA0 is the number of particles with a particle size of 0.5 μm or larger contained in the composition at the first time point (0 second) when obtaining the composition, and EA1 is the number of particles with a particle size of 0.5 μm or larger contained in the composition after storing the composition at a temperature condition of about -17 °C for 30 days from the first time point (0 second).

[0131] Specifically, under the condition of particles with a size of 1000 μm or less at 23 °C, use a liquid particle sensor (KS-42B, Rion Co., Ltd., light source wavelength is 780 nm, light source output is 40 mW, flow rate is 10 mL / minute, maximum number of particles is 1200 / mL, simultaneous measurement loss is 5%, DC12V) to measure the number of particles in five channels of 0.2 μm or larger, 0.3 μm or larger, 0.5 μm or larger, 1.0 μm or larger, and 2.0 μm or larger, and then the number of particles can be calculated by adding up all the numbers of particles measured in the channels of 0.5 μm or larger, 1.0 μm or larger, and 2.0 μm or larger. Refer to the data in Table 2 for the test results.

[0132] 3) Long-term AC driving test

[0133] Preparation of FFS-driven liquid crystal display panel:

[0134] Provide a first substrate, which is a glass substrate with a size of 30 mm × 35 mm and a thickness of 0.7 mm, including a thin-film transistor layer;

[0135] Form a counter electrode on the first substrate. The counter electrode is a patterned full-surface ITO electrode;

[0136] Form an insulating layer on the counter electrode. The insulating layer can be a silicon nitride (SiN) film prepared by chemical vapor deposition (CVD). The film thickness of the SiN film is 500 nm;

[0137] Form a pixel electrode on the insulating layer. The pixel electrode is a patterned ITO electrode with a comb-like shape. Please refer to Figure 5 and Figure 6 , the pixel electrode 105 includes two types, the first pixel 1051 and the second pixel 1052. The size of each pixel is 10 mm in length and about 5 mm in width. The pixel electrode 105 and the counter electrode 106 are electrically insulated due to the action of the insulating layer 107. The pixel electrode 105 has a comb shape with multiple electrode elements having a width of 3 μm bent at a central inner angle of 160° arranged at intervals of 6 μm and in parallel. One pixel has a first region 1053 and a second region 1054 with a line connecting the bent portions of multiple electrode elements as the boundary. The formation directions of the electrode elements of the pixel electrodes in the first region 1053 and the second region 1054 of each pixel are different. That is, in the case of taking the rubbing direction of the alignment film as a reference, in the first region 1053, the electrode elements of the pixel electrode are formed at an angle of +10° (clockwise), and in the second region 1054, the electrode elements of the pixel electrode are formed at an angle of -10° (clockwise). That is, in the first region 1053 and the second region 1054 of each pixel, the rotation action directions of the liquid crystal induced by applying a voltage between the pixel electrode 105 and the counter electrode 106 in the plane of the substrate are in opposite directions;

[0138] Form an alignment film above the pixel electrode. Specifically, coat the composition for preparing the alignment film above the pixel electrode to form a uniform thin film of 100 nm, and irradiate it with linearly polarized ultraviolet light with a wavelength of 254 nm and an illumination intensity of 500 mJ / cm 2 , and further bake it to obtain the first substrate with the first alignment film;

[0139] Provide a second substrate, which is a glass substrate, including a color filter layer;

[0140] A second alignment film is formed on the second substrate to obtain a second substrate with the second alignment film, and the method is referred to the preparation of the first alignment film above;

[0141] The above-mentioned first substrate with the first alignment film and the second substrate with the second alignment film are taken as a group. At a position other than the liquid crystal injection port, a sealant is printed on the first substrate and / or the second substrate. Then, the first substrate and the second substrate are bonded in such a way that the first alignment film and the second alignment film face each other and the rubbing directions are anti-parallel. Then, the sealant is cured to fabricate an empty liquid crystal cell with a cell gap of 3.5 μm. Next, a negative liquid crystal MLC 2767 (manufactured by Merck) is injected into the empty liquid crystal cell by a reduced-pressure injection method, and the injection port is sealed to obtain an FFS-type liquid crystal display panel.

[0142] Evaluation of afterimage caused by long-term AC driving: The liquid crystal display panel fabricated by the above method is placed in a constant-temperature environment at 60 °C, and an AC voltage of ±6 V is applied at a frequency of 60 Hz for 120 hours. Then, a short circuit is formed between the pixel electrode and the counter electrode of the liquid crystal display panel, and it is left at room temperature for one day. Next, two polarizers arranged with their polarization axes orthogonal are set on the opposite sides of the liquid crystal display panel, and the backlight is turned on in a state without voltage application, and the configuration angle of the liquid crystal display panel is adjusted so that the brightness of the transmitted light becomes the minimum. Finally, the rotation angle when the liquid crystal display panel is rotated from the angle where the second region of the first pixel is the darkest to the angle where the first region of the first pixel is the darkest is taken as the angle Δ. Similarly, in the second pixel, the second region and the first region are compared, and the same angle Δ is calculated.

[0143] Table 2 Composition and performance data of the alignment film

[0144]

[0145]

[0146] Among them, the alignment film PI-1 does not add an alignment film additive, the alignment film PI-2 adds the alignment film additive Add-1 provided in this application, and the alignment film PI-3 adds a crosslinking additive Add-2 in the related art. The structure of Add-1 contains a liquid crystal-like structure and a Si-containing protecting group, and the structure of Add-2 does not contain a liquid crystal-like structure and a Si-containing protecting group.

[0147] It can be seen from the data in Table 2 that the pencil hardness of the alignment film PI-2 and the alignment film PI-3 is higher than that of the alignment film PI-1, which proves that the mechanical hardness of the polyimide alignment film can be effectively improved after adding the alignment film additive.

[0148] As can be seen from the data in Table 2, the AC afterimage result of the alignment film PI-2 is significantly lower than that of the alignment film PI-1, and the AC afterimage result of the alignment film PI-3 is significantly higher than that of the alignment film PI-1. Since the smaller the AC afterimage result indicates that the rotation angle of the liquid crystal is smaller under the same conditions, the better the alignment effect of the alignment film on the liquid crystal. Therefore, the alignment property of the alignment film PI-3 on the liquid crystal decreases, while the alignment property of the alignment film PI-2 with the alignment film additive of the present application on the liquid crystal is effectively improved.

[0149] As can be seen from the data in Table 2, the change in the number of particles of the alignment film PI-2 relative to the alignment films PI-1 and PI-3 is significantly reduced. Since the smaller the number of particles indicates that the amount of precipitated substances in the composition is small under the same time storage conditions, its storage stability is better. Therefore, the stability and reliability of the composition with the alignment film additive of the present application are significantly improved.

[0150] Therefore, adding the alignment film additive of the present application to the polyimide alignment film can effectively improve the mechanical hardness of the alignment film and its alignment property on the liquid crystal, effectively improve the afterimage caused by long-term AC driving, and significantly improve the long-term storage stability of the composition for forming the alignment film.

[0151] The present application provides an alignment film additive, an alignment film, and a liquid crystal display panel. The alignment film additive provided by the present application has the structure shown in Formula I. The structure of Formula I is an amide compound, including an amide group. The amide group can undergo a polymerization reaction with the precursor polyamic acid of polyimide to form a cross-linked structure between polyamic acid molecules, thereby improving the hardness of the alignment film. A liquid crystal-like structure A is connected between the two amide groups in the structure of Formula I. The liquid crystal-like structure A can improve the liquid crystal anchoring force of the alignment film, thereby improving the liquid crystal alignment performance of the alignment film. The ends of the structure of Formula I are designed with protecting groups G1, G2, G3, and G4. The protecting group is a silyl group that can be removed under heating conditions. When the alignment film is heat-treated, the protecting groups at the ends of the alignment film additive desorb and break at high temperature, exposing the -O- at the ends. The -O- combines with -H to restore the cross-linking effect, and the cross-linking reaction can proceed smoothly. At a relatively low temperature, the protecting groups at the ends of the alignment film additive will not be removed, thereby inhibiting the cross-linking reaction and reducing the formation of unnecessary cross-linked structures to improve the stability and reliability of the alignment film composition. Therefore, the alignment film additive provided by the present application can improve the mechanical strength of the alignment film while enabling the alignment film to have a high alignment property, and can improve the reliability and stability of the alignment film. In the above embodiments, the descriptions of each embodiment have their own focuses. For the parts not detailed in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0152] Among the embodiments, implementation manners, and related technical features of the present application, they can be combined and replaced with each other without conflict.

[0153] The above are only the preferred embodiments of the present application and do not impose any formal restrictions on the present application. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still fall within the scope of the technical solution of the present application.

Claims

1. An alignment film additive, characterized in that, The alignment film additive has a structure shown in Formula I: Wherein, A is selected from the groups represented by Formula II, Selected from a benzene ring, cyclohexane or cyclohexene, any H thereon is unsubstituted or substituted with F, Cl, Br, -OH, an alkyl group having 1-10 carbon atoms, or an alkoxy group having 1-10 carbon atoms; Z1, Z2, Z3, Z4, Z5 are selected from a single bond, -O-, -S-, -CO-, -C(O)O-, -OC(O)-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, and an alkylene group having 1 to 10 carbon atoms, and one or more H in Z1, Z2, Z3, Z4, and Z5 are unsubstituted or substituted by F, Cl, Br, or I; n and m are selected from integers from 0 to 10, and n + m ≥ 1; B1, B2, B3, B4 are selected from alkylene groups having 1 to 5 carbon atoms; G1, G2, G3, G4 include a silyl group.

2. The alignment film additive according to claim 1, wherein G1, G2, G3, G4 are selected from the groups represented by Formula III, Wherein, R1, R2, R3 are selected from alkyl groups having 1 to 10 carbon atoms.

3. The alignment film additive according to claim 2, wherein R1, R2, R3 are selected from methyl groups.

4. The alignment film additive according to claim 1, characterized in that, A is selected from the groups represented by Formula II-1: Wherein, Z1 is selected from a single bond, -O-, -CO-, -C(O)O-, -OC(O)-, -CH2O-, -OCH2-, and an alkylene group having 1 to 5 carbon atoms, and one or more H in Z1 are unsubstituted or substituted by F, Cl, Br, or I; n and m are selected from 1, 2, or 3; p and q are selected from 1, 2, 3, 4, or 5.

5. The alignment film additive according to claim 1, characterized in that, A contains at least one of a phenoxy group and a biphenyl group.

6. The alignment film additive according to claim 1, characterized in that, In the structure of Formula I, G1-O-B1 and B2-O-G2 are symmetric with respect to A, and G3-O-B3 and B4-O-G4 are symmetric with respect to A.

7. The alignment film additive according to claim 1, wherein The alignment film additive has a structure shown in Formula I-1:

8. An alignment film, characterized in that, The alignment film is formed from a composition including an acid anhydride, a diamine, and the alignment film additive according to any one of claims 1 to 7.

9. The alignment film according to claim 8, wherein The alignment film additive accounts for 0.1 wt% to 10 wt% of the total mass of the acid anhydride and the diamine.

10. A liquid crystal display panel, characterized in that, Including: A first substrate; A second substrate disposed above the first substrate, and the second substrate is disposed opposite to the first substrate; A liquid crystal layer disposed between the first substrate and the second substrate; A first alignment film disposed between the first substrate and the liquid crystal layer; And A second alignment film disposed between the second substrate and the liquid crystal layer; Wherein, the first alignment film and the second alignment film are the alignment films according to any one of claims 8 to 9.

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